Therapeutic agents may be delivered to a targeted location in a human utilizing a number of different methods. For example, agents may be delivered nasally, transdermally, intravenously, orally, or via other conventional methods. Delivery may vary by release rate (e.g., quick release, slow release, or biphasic release). Delivery may also vary as to how the drug is administered. Specifically, a drug may be administered locally to a targeted area, or administered systemically.
With systemic administration, the therapeutic agent is administered in one of a number of different ways including orally, inhalationally, or intravenously to be systemically processed by the patient. However, there are drawbacks to systemic delivery of a therapeutic agent, one of which is that high concentrations of the therapeutic agent travel to all portions of the patient's body and can have undesired effects at areas not targeted for treatment by the therapeutic agent. Furthermore, large doses of the therapeutic agent only amplify the undesired effects at non-target areas. As a result, the amount of therapeutic agent that results in application to a specific targeted location in a patient may have to be reduced when administered systemically to reduce complications from toxicity resulting from a higher dosage of the therapeutic agent.
An alternative to the systemic administration of a therapeutic agent is the use of a targeted local therapeutic agent delivery approach. With local delivery of a therapeutic agent, the therapeutic agent is administered using a medical device or apparatus, directly by hand, or sprayed on the tissue, at a selected targeted tissue location of the patient that requires treatment. The therapeutic agent emits, or is otherwise delivered, from the medical device apparatus, and/or carrier, and is applied to the targeted tissue location. The local delivery of a therapeutic agent enables a more concentrated and higher quantity of therapeutic agent to be delivered directly at the targeted tissue location, minimizing or eliminating broader systemic side effects. With local delivery, the therapeutic agent that escapes the targeted tissue location dilutes as it travels to the remainder of the patient's body, substantially reducing or eliminating systemic effects.
Local delivery is often carried out using a medical device as the delivery vehicle. One example of a medical device that is used as a delivery vehicle is a stent. Boston Scientific Corporation sells the Taxus® stent, which contains a polymeric coating for delivering Paclitaxel. Johnson & Johnson, Inc. sells the Cypher® stent which includes a polymeric coating for delivery of Sirolimus.
In applying coatings to medical devices, such as stents and catheters, coverage and uniformity are important factors in getting optimal performance out of the coated medical device. If a device does not have the desired coverage then there may be areas on the device that do not have proper coating which can lead to problems. Similar problems can arise when the coating is not uniform. Non-uniform coatings can cause inconsistent interactions, especially when a therapeutic agent is being delivered. Ideally, the coating should be uniform over the desired portions of the medical device so that dosage and interaction with tissue can be better controlled.
Degradation of coating materials, and the therapeutic agents that can be included in coating materials, is a significant concern in the area of coated medical devices. Multiple strategies have been employed to prevent degradation of coating materials. An outer layer of porous biocompatible polymer covering the therapeutic coating layer has been used to control the release of the active agent and to reduce degradation of the therapeutic coating layer. The curing of coating materials by applying heat, UV light, chemical cross-linker, and/or reactive gas has also been used to reduce degradation of the coating. Unfortunately, curing a coating can reduce its therapeutic effectiveness.
In both of the aforementioned techniques, the coating material is deposited onto the medical device long before the device will be implanted into the patient. Normally, the coated device would be manufactured, packaged, and then sent to another location and stored before use. The aforementioned techniques were designed to preserve the coating material already deposited on the medical device for the long period of time between when the device is coated and when the device is implanted (typically a week to months). Preserving a coating material that is already applied to a device is difficult, in part, because the thin coating layer provides a large surface area for interaction with the surrounding environment and because oxygen, and other elements that may cause degradation, only need to diffuse a short distance through the thickness of the coating to reach all of the coating material.
A need exists for an apparatus to uniformly apply a coating material, which has been stored and optionally preserved from degradation, to a medical device shortly before the device is implanted into a patient.